This invention relates to a stator of a variable-geometry axial turbine for aeronautical applications and, in particular, for aeronautical engines.
As is known, an axial turbine for an aeronautical engine determines an annular duct with increasing diameter and comprises at least one stator and one rotor arranged axially in succession to each other, and comprising respective arrays of airfoil profiles housed in the annular duct and between them circumferentially delimiting associated spaces through which a flow of gas can pass.
In aeronautical engines, it has been found necessary to use axial turbines having the highest possible efficiency in all operating conditions and, therefore, over a relatively wide range of values for the rate of flow of the gases that pass through the turbine itself.
This requirement could be met by producing variable-geometry turbines, i.e. turbines comprising at least one stator in which, in use, it is possible to vary the transverse area of the associated spaces, in particular by adjusting the angular position of the airfoil profiles about respective axes incident to the axis of the turbine.
In stators of axial turbines of known type, the annular duct is delimited radially by conical surfaces while the airfoil profiles have a relatively long length in the direction of travel of the gases, because of which any displacement of these profiles would cause jamming against the above-mentioned conical surfaces or else excessive radial clearances and therefore considerable leakage of gas between adjacent spaces, because of which the flow of the gases in the spaces themselves would become non-uniform, with a consequent drastic reduction in the efficiency of the turbine.
The purpose of the invention is to produce a stator of a variable-geometry turbine for aeronautical applications, which enables the problems set out above to be solved simply and functionally.
According to the present invention, a stator of a variable-geometry axial turbine for aeronautical applications is produced; the stator having an axis and comprising an annular duct delimited radially by an annular outer and an annular inner surface; an array of airfoil profiles housed in the duct in positions angularly equidistant from each other about said axis and each comprising an associated pair of end edges opposite each other and coupled with said outer and inner surfaces, characterised in that said airfoil profiles are rotatable with respect to said outer and inner surfaces about respective axes of adjustment incident to said axis, and in that it comprises means for maintaining said airfoil profiles a predetermined clearance from said outer and inner surfaces to maintain a substantially constant clearance between said outer and inner surfaces and said end edges when the angular position of said airfoil profiles is varied.